Every year, over 10 million tons of peanut waste accumulate globally, primarily as discarded shells. Scientists have now found a way to transform this biomass into carbon materials similar to graphene.
Graphene, a carbon-based material often lauded as a ‘wonder’ material, is known for its exceptional strength, lightweight nature, and conductivity of heat and electricity. Its current applications are broad, with potential to greatly enhance consumer electronics.
However, producing graphene at scale remains challenging and costly, which makes alternative production techniques potentially transformative for energy systems, data storage, and other technologies.
Researchers at the University of New South Wales (UNSW) in Australia have demonstrated that peanut shells can enhance graphene production in a more cost-effective and environmentally friendly manner compared to traditional methods.
UNSW mechanical engineer Guan Yeoh explains, “Most of the waste from the shell is either discarded or recycled into low-value applications that don’t maximize their full potential.” Yeoh states that their research shows peanut shells can be converted into high-quality graphene using less energy and without chemicals, offering environmental benefits.
The process relies on lignin, a natural polymer rich in carbon found in most plants. Although its presence in peanut shells was known, the challenge was determining the optimal processing method.
The team explored several methods to prepare the shell waste for lignin extraction before applying a method called flash joule heating (FJH). This process involves a rapid electrical pulse raising temperatures to over 3,000 degrees Celsius (5,432 degrees Fahrenheit) in milliseconds, reorganizing carbon atoms into graphitic structures, including few-layer turbostratic graphene.
While FJH was central to the process, the preparation of the shells was key. The researchers discovered that a staged pretreatment involving indirect Joule heating at around 500 °C for five minutes, followed by a brief higher-temperature step, was the most effective method.
This pretreatment removed impurities and converted the shells into char, a carbon-rich and conductive material.
“This process is essential to eliminate impurities and provide the best carbon-rich material, ensuring minimal defects in the final graphene, which should be a single layer of atoms,” Yeoh says.
Previous attempts have been made to convert peanut shells to graphene, but this research underscores the importance of carefully controlling the precursor material to enhance graphene quality.
Related: ‘Wonder Material’ Graphene Has Been Discovered on The Moon
The process is not without its challenges. While the resulting graphene is high-quality, it often consists of several layers in a turbostratic arrangement. The technique may require three to four years to become commercially viable, the researchers note.
As efforts to refine this laboratory-based concept continue, the team is also exploring if their preparation and heating methods could be applied to other biomass types.
“We plan to experiment with other materials, such as coffee grounds or banana peels, to find effective char sources for graphene production,” says Yeoh. “Given the abundance of organic materials, our work shows a promising balance of energy efficiency, graphene quality, and economic viability.”
The study is detailed in the Chemical Engineering Journal Advances.
